1. Field of the Invention
The present invention relates to an automatic transmission for an automobile and more particularly to an automatic transmission whose torque converter incorporating a part or the whole of a forward and reverse changeover apparatus therein.
2. Prior Art
Generally, an automatic transmission having a continuously variable transmission comprises a starting apparatus for controlling a power transmission from an engine to a transmission on starting, a forward and reverse changeover apparatus for reversing the rotational direction of a drive shaft in order to propel a vehicle in the reverse direction and a clutch section for changing over driving force supplied to the forward and reverse change over apparatus.
FIG. 4 shows a skeleton of a conventional continuously variable automatic transmission 1 in which a torque converter is used as a starting apparatus.
The continuously variable automatic transmission 1 comprises a starting apparatus 2 connected to an engine 25, a continuously variable transmission 3, a forward and reverse changeover apparatus 4 interposed between the starting apparatus 2 and the continuously variable transmission 3. The forward and reverse changeover apparatus 4 includes a forward clutch 5 for connecting and disconnecting a transmission of driving force from the starting apparatus 2, a planetary gear 6 for reversing the driving force from the starting apparatus 2 and a reverse brake 7 for operating and stopping the planetary gear 6.
At a forward running, a clutch plate 5a of the forward clutch 5 is in the engagement condition where the driving force from the starting apparatus 2 is transmitted to a pulley input shaft 3b connected to a primary pulley 3a of the continuously variable transmission 3 through a clutch drum 5b and a clutch hub 5c. When starting, power is transmitted to the clutch drum 5b through a working fluid of a torque converter 2a in the starting apparatus 2. After being transferred to a normal running, a lock-up clutch 2b is engaged to transmit the driving force of the engine 25 directly to the clutch drum 5b without going through the torque converter 2a.
On the other hand, at a reverse running, the clutch plate 5a is disengaged and at the same time a brake plate 7a of the reverse brake 7 is engaged. As a result, a ring gear 6a of the planetary gear 6 is fixed to the transmission case and a double-arranged planetary pinion 6c supported by a planetary carrier 6b which is connected with the clutch drum 5b, rotates a sun gear 6d connected with the pulley input shaft 3b in the reverse direction at a reduced speed.
FIG. 5 shows an example of the case where the engine 25 and the automatic transmission 1 are arranged transversely, in which an overall width W.sub.s of the combination of the engine 25 and the automatic transmission 1 must be of a size capable of accommodating the engine 25 and the automatic transmission 1 in an engine room 8a.
Recent motor vehicles have a frame 9 on both sides of the engine room 8a respectively in order to absorb an impact in case the vehicle has a collision. Furthermore, a front tire 10 is arranged outside of the frame 9, respectively.
The frame 9 must have a certain amount of sectional area sufficient to have rigidity for securing a safety on impact and also the front tire is required to move within as large steering angle as possible in order to obtain a small turning circle radius. Further, recent motor vehicles have a tendency to reduce the width of the vehicle body due to a necessity of improving fuel economy.
As a result of this, a space for accommodating the engine 25 and the transmission 1 in the engine room 6a tends to decrease, therefore the overall width W.sub.S of the combination of the engine and transmission is required to be shortened as far as possible. One idea for realizing this is to reduce a widthwise size W.sub.T of the automatic transmission 1 itself.
However, in the conventional automatic transmission 1, since the starting apparatus 2, the forward and reverse changeover apparatus 4 and the transmission 3 are arranged in a power transmitting order, it is technically difficult to reduce the size W.sub.T in the axial direction of the automatic transmission 1.
That is, in order to reduce the size W.sub.T in the axial direction of the automatic transmission 1 arranged in this manner, several means such as decreasing the pulley ratio of the continuously variable transmission, reducing the width of a belt wound around both pulleys, closing clearances between components or the like can be considered. However, any of these means may adversely affect the function of the automatic transmission 1 or may reduce the rigidity and strength of the transmission 1.
To solve this, for example, UK Patent Application Laid-Open No. 2033029A discloses a technique in which a fluid coupling is employed as a starting apparatus and a planetary gear of the forward and reverse changeover apparatus is accommodated in an inner diameter portion (on the engine side) of the fluid coupling in order to shorten the axial length of the automatic transmission.
However, since the fluid coupling inherently does not have a torque amplifying effect, some other means for amplifying torque are additionally needed, this resulting in the complicated construction of the automatic transmission.
Further, according to this prior art, since the reverse brake mechanism for reversing the planetary gear is arranged between the fluid coupling and the continuously variable transmission and the carrier of the planetary gear is connected with the brake plate of the reverse brake mechanism through a sleeve, the construction is not only complicated, but also the axial length of the automatic transmission is elongated due to the reverse brake mechanism provided between the fluid coupling and the continuously variable transmission.
In general, the torque converter is used more often for the starting apparatus of the continuously variable transmission than the fluid coupling is done, mainly because a stator incorporated in the torque converter serves as amplifying torque when the vehicle starts from the idling condition of the engine.
However, in case where the torque converter is introduced in a place of the fluid coupling, the stator make it difficult to secure a space for accommodating the planetary gear in the inner diameter position of the torque converter, thereby it is technically difficult to reduce the axial size of the automatic transmission.